Add header break to table

Author: odow

README.md

@@ -219,6 +219,7 @@ the node in `"node_list"`.
 ##### Other nodes
 
 | Name | Arity |
+| ---- | ----- |
 | `"log"` | Unary |
 | `"log10"` | Unary |
 | `"exp"` | Unary |

readme_builder/readme_builder.go

@@ -156,7 +156,8 @@ func processNonlinear(data map[string]interface{}) string {
 	functionStrings := []string{
 		"##### Functions",
 		"",
-		"| Name | Arity |"}
+		"| Name | Arity |",
+	    "| ---- | ----- |"}
 
 	leafStrings := []string{
 		"#### Nonlinear functions",